The present invention relates generally to an improved composition and method for preserving metal reinforced concrete structures, and more particularly to such a composition and method specifically adapted for application as a fiber or filament (hereinafter fiber/filament) blended with a selected migratory corrosion inhibitor and disposed within the encapsulating sheath of posttensioning cables utilized in such concrete structures. Posttensioning cables are used for the purpose of compressing cast concrete beams or other structural members to impart the characteristics of pre-stressed concrete to these members.
The compositions of the present invention employ an impregnated fiber or filament in combination with posttensioning cable reinforcements, with the impregnated filament being disposed within the confines of the cable-enclosing sheathing, thereby providing for long-term protection of the metallic cable components within what may otherwise be a hostile environment. Posttensioning cables may be employed in combination with the compositions disclosed in co-pending application Ser. No. 09/861,906, now U.S. Pat. No. 6,764,615, and entitled “MIGRATORY CORROSION INHIBITOR FIBERS”, with the formulations of the present invention enhancing the protection available to the posttensioning cables. The mixtures or blends disclosed in application Ser. No. 09/961,906 now U.S. Pat. No. 6,764,615, are particularly adapted for repairing the surfaces of concrete structures, while at the same time for use in passivating and otherwise protecting the surfaces of metal reinforcements present in damaged concrete structures over extended periods of time. The system of the present invention may be utilized in combination with such mixtures or blends. The environmentally friendly migratory corrosion inhibitors are preferably a mixture of sodium benzoate and an alkali metal sebacate such as sodium sebacate and/or potassium sebacate. In accordance with the present invention, the migratory corrosion inhibitors may be present as an impregnant in the oriented filaments or fibers disposed within the cable-enveloping sheath, with such material being typically in addition to any inhibitors that may be present in the mortar/aggregate blend. An inhibitor source may be contained in an extruded reinforcing plastic fiber comprising a polymeric resin matrix into which a quantity of the migratory corrosion inhibitors set forth above has been co-extruded. It will be appreciated that the posttensioning cable reinforcement preservation features of the present invention may be applied to a wide variety of structures, including those which include various types of posttensioning cable reinforcement. Those of skill in the art will, of course, be able to select the appropriate cable for given applications.
The migratory corrosion inhibitors present in the improved formulation, preferably sodium benzoate and sodium sebacate are supplied as an impregnant in the fiber disposed within the confines of the sheathing envelope of posttensioning cable, with the migratory corrosion inhibitors being released from the fiber to the metallic cable over a relatively extended period of time. The inhibitor formulation is suited for co-extrusion with reinforcing fibers or filaments, and may be employed in combination with such filaments fabricated from synthetic resins such as polyethylene, polypropylene, nylon, polyethylene terephthalate, as well as others.
The fiber or filament forming composition is typically prepared in a form where it may be added or blended with the fiber or filament matrix material held within the extrusion barrel of a typical filament extruder. The inhibitor material, as co-extruded, impregnates the fiber and is present at the time the fiber is oriented subsequent to exiting the extruder. Typically, the formulations of the present invention include between about 5% and 10% by weight of migratory corrosion inhibitor, balance resin. For most applications, polyethylene, polypropylene, nylon such as Nylon 66 or Nylon 6 are suited for this application, as well as those fabricated from polyethylene terephthalate. The high temperature properties of the selected inhibitors are such that they provide compatability with the plastic resin matrix. The fiber or filament forming composition is typically prepared in two components consisting of the plastic resin and plastic resin substrate forming material. The blend is then co-extruded as an impregnated fiber or filament. Prior to extrusion, the blends are mixed together to form the extrudate which is then ready.
Following extrusion, the fiber or filament is cooled, and thereafter oriented to a typical extent or degree. Since the fibers retain a substantial amount of their tensile properties, typical orientation procedures may be utilized, typically an elongation of 200%. These fibers have excellent durability and are resistant to water and/or carbonation attack. In addition to these mechanical properties, the impregnated fibers or filaments provide excellent corrosion protection to the metallic reinforcement contained within the sheathed posttensioning cable, thus extending the longitivity of these components. The compositions of the present invention accordingly increase the quality, integrity, and also extend the life of the cable structure.
The inhibitors which have been incorporated directly into the co-extruded fiber generally evolve slowly. These molecules migrate to provide ongoing protection to the metallic cable. The inhibitors selected for the current application possess the characteristic of being able to migrate from the impregnated filament onto and along the surfaces of the metallic members. The corrosion inhibitors present in the sheathed or encapsulated cable deliver long-term corrosion protection by retarding the rate of corrosion on the steel cable reinforcements.
The migratory corrosion inhibitor impregnated fiber/filament components may extend continuously as a single component along the entire length of the cable, or alternatively inserted as individual segments or components of shorter length. When an array of components is utilized, it is generally desirable to have at least one such fiber/filament present at all points along the extent of the posttension cable being protected.
As indicated hereinabove, the source of migratory corrosion inhibitors is from an extruded fiber or filament comprising a polymeric resin matrix into which a quantity of migratory corrosion inhibitors has been co-extruded. The co-extruded inhibitors preferably include sodium benzoate and sodium sebacate.
Thus, the composition and methods of the present invention provide a medium for ongoing metallic surface protection through extended delivery of migratory corrosion inhibitors to and throughout the length of the cable. The features of the invention are achieved through the addition of these impregnated fibers or filaments directly to the interior or confines of the sheathed cable, with the utilization providing extended long-term corrosion inhibitor availability.
The improved composition and method of application in accordance with the present invention offers engineers, property owners, contractors, DOTs and other governmental agencies a corrosion inhibiting technology adapted to extend the life of concrete structures employing posttensioning cables The composition and formulations of the present invention enable the artisan to employ these reinforcements in a wider variety of structures. Because of the nature of the improved compositions, the corrosion inhibited tensioned cables may be employed in a conventional manner.
Because of their physical and chemical nature, the migratory corrosion inhibitors present in the formulations, form a protective layer or deposit directly onto metallic surfaces. In addition to those areas which are in direct contact with the impregnated fiber or filament, the migratory properties of the inhibitors extend protection to metallic surfaces surrounding or otherwise spaced from the impregnated fiber, such as in and around the core or axis. In addition to protection afforded the metallic components, the inhibitors may protect the surface of the concrete immediately adjacent the sheath against further carbonation or attacks by chlorides and/or acid rain.
Given the advantageous features of the working formulations of the present invention, the posttensioned cables may be utilized in a variety of concrete structures. Such structures include, by way of example, steel-reinforced concrete bridges, parking decks, ramps, and garages exposed to corrosive environments such as carbonation, deicing salts, and possible atmospheric attack. In general, these cables may be utilized to enhance the useful life of virtually any type of reinforced concrete, commercial and/or civil engineered structures.